ISS Astronauts Age 20-25 Microseconds Slower Per Day as Speed Outweighs Weaker Gravity
Updated
Updated · spacedaily.com · Jul 9
ISS Astronauts Age 20-25 Microseconds Slower Per Day as Speed Outweighs Weaker Gravity
1 articles · Updated · spacedaily.com · Jul 9
Summary
Astronauts in low Earth orbit return slightly younger than people on Earth, with ISS crews aging about 20-25 microseconds less per day and roughly 4-5 milliseconds less over six months.
At about 400 kilometers up, weaker gravity makes station clocks run a little faster, but the ISS travels near 7,700 meters per second—about five miles per second—so special relativity produces a larger slowing effect.
NASA says the station circles Earth every 90 minutes, and that net lag is measurable with precise clocks even though it is medically irrelevant compared with radiation, microgravity, bone loss and muscle loss.
The effect is long established: 1971 atomic-clock flights matched relativity predictions, and GPS satellites still require constant timing corrections because tiny clock errors can become large position errors.